The present invention generally relates to an internal combustion engine and in particular, to an engine with excellent lubricity suitable for a power source of a small working machine including but not limited to a portable trimmer, a lawn mower, a chain saw or the like.
A portable type working machine represented by a portable trimmer as well as a chain saw is required to allow an operator to work without any restrictions on his working posture. Accordingly, an internal combustion engine as a power source mounted on such working machine must provide stable operation even if the machine is used in the working posture of, for example, a laterally tilted position.
In order to meet this requirement, there has been employed conventionally a compact air-cooled type two-stroke cycle gasoline engine (hereafter, the xe2x80x9ctwo-stroke cycle enginexe2x80x9d) equipped with a diaphragm carburetor, which uses a mixed fuel oil composed of fuel and lubricant oil mixed at a certain ratio. The two-stroke cycle engine of this type, however, has a disadvantage in that it is difficult to reduce the exhaust gas or an emission gas since the exhaust gas therefrom contains a fair amount of unburned gas constituent due to a gas-flow type scavenging system employed therein.
As for other measures taken to reduce the emission gas, a four-stroke cycle internal combustion engine (Otto engine) has advantage over the two-stroke cycle engine because the former generates a small amount of unburned gas. Therefore, the four-stroke cycle engine has been looked into for employment in the portable working machine in place of the two-stroke cycle engine. The four-stroke cycle engine typically has an oil reservoir formed by an oil pan disposed in a bottom portion of a crank chamber accommodating a crankshaft, and employs a lubrication system in which a lubricating oil contained in this oil reservoir is pumped up by a pump and/or is splashed up by a rotary member, typically, so-called xe2x80x9can oil dipperxe2x80x9d (Japanese Patent Laid-Open Disclosure No. Hei 9-177528).
Further, Japanese Patent Laid-Open Publications No. Hei 10-288019 and No. Hei 10-288020 disclose a system in which two communicating channels are provided between a crank chamber and an oil reservoir so as to allow them to communicate with each other, and an open/close valve constructed substantially by a channel formed inside a crankshaft is provided in one of the communicating channels. In the other communicating channel, a reed valve is installed so that, when the pressure in the crank chamber is made negative with the upward motion of an ascending piston, the open/close valve is opened and the reed valve is closed, whereby the oil in the oil reservoir is supplied into the crank chamber through the one communicating channel. On the other hand, when the pressure in the oil reservoir is made positive with the downward motion of a descending piston, the open/close valve is closed and the reed valve is opened and whereby the pressure in the oil reservoir is made positive.
Further, Japanese Patent Laid-open Publication No. Hei 9-170417 discloses a lubrication system in which a crank chamber and an oil reservoir always communicate with each other, a valve chamber (pressure regulating chamber) located adjacent to the crank chamber is made to communicate with a valve gear chamber (the pressure therein is maintained to be substantially equal to atmospheric pressure), and a reed valve is disposed in a communicating channel between the valve space and the crank chamber, so that the reed valve is opened when the pressure in the crank chamber is being raised while a piston descends. The lubrication system disclosed in this Japanese Patent Laid-open Publication Disclosure No. Hei 9-170417 draws the engine oil within the oil reservoir into the crank chamber by always maintaining a negative pressure condition inside the crank chamber.
A lubrication system using the oil pump, however, is not suitable for an engine of the portable working machine since an additional mechanism for discharging and recovering the lubricating oil has to be employed and thus would make the system complicated and heavy. On the other hand, a lubrication system using the oil dipper has shortcomings as well in that it is difficult to determine a length of the oil dipper during a designing stage of the engine. That is, if the length of the oil dipper is designed to be too short, a desired degree of oil lubrication may become difficult to be supplied by the oil dipper within a short period of time after starting due to an oil consumption. On the contrary, if the length of the oil dipper is designed to be too long, a large amount of oil may be splashed up by the oil dipper immediately after the oil has been filled into the oil pan making a mist of oil in the crank chamber too rich (to reach to excessive level) possibly resulting in a problematic level of pollution created by the blow-by gas.
Further, although either lubrication system disclosed in Japanese Patent Laid-open Publications No. Hei 10-288019, Hei 10-288020, or Hei 9-170417 uses a check valve such as a reed valve as an indispensable component, the reed valve is likely to result in problems associated with its durability since this type of engine is driven at an extremely high speed, that is, even the normal revolution number of which is as high as 7500 rpm, and in addition, there is another risk in the high revolution driving range that the valve may possibly fail to operate as intended in the design stage because the valve is likely to be kept substantially open all the time.
The present invention has been devised during a process in the technology development activity attempting to improve the lubrication system of an oil dipper type engine in response to the present environmental and social concerns surrounding the engine for use as a portable working machine.
An advantage of the present invention is to provide an internal combustion engine with an innovative lubrication system different from the conventional one.
Another advantage of the present invention is to provide an internal combustion engine in which the amount of oil in a crank chamber can be optimized while making an engine lubrication structure simpler.
Another advantage of the present invention is to provide an internal combustion engine which does not require use of a check valve, such as a reed valve, as an indispensable component thereof.
Another advantage of the present invention is to provide an internal combustion engine which can effectively lubricate itself without requiring another power source.
According to the present invention, the technological advantages described above can be achieved by an innovative internal combustion engine, comprising: a crankshaft; a crank chamber accommodating the crankshaft; an oil reservoir arranged adjacent to the crank chamber; with the crank chamber and the oil reservoir being in communication with each other via a communicating channel having a flow resistance, so that the flow resistance in the communicating channel causes a pressure in the oil reservoir to change with a delay with respect to the change of a pressure in the crank chamber, the pressure difference between the crank chamber and the oil reservoir causing a fluid flow through the communicating channel between the crank chamber and the oil reservoir.
In an exemplary embodiment of the present invention, the crank chamber and the oil reservoir are separated from each other by a partition wall, and the communicating channel having the flow resistance is a small hole formed in the partition wall.
Further, in addition to this small hole, a suction tube extending from the partition wall into the engine oil in the oil reservoir may be provided on the partition wall so that the crank chamber may communicate with the oil reservoir through the suction tube and the small hole.
Since the suction tube extends into the engine oil in the oil reservoir, the oil is supplied as liquid through the suction tube into the crank chamber. The engine oil supplied into the crank chamber is then atomized by a rotating member such as the crankshaft or the like disposed in the crank chamber.
Other advantages, features and effects of the present invention will be more fully apparent from a reading of the following detailed description of preferable embodiments in conjunction with the accompanying drawings.